6io FOOT AND STROBELL. [Vol. XVI. 



which have reached the inner pole of the second spindle, the 

 rays of the aster still persisting. A comparison with photo. 23 

 indicates that these ring chromosomes have been formed by 

 the uniting of the free ends of F-shaped chromosomes, such 

 as those shown in photo. 23. 



Photo. 25 shows two (of the eleven) chromosomes at a little 

 later stage of development. Besides the ring, a tiny spherical 

 body appears in connection with each chromosome, and we 

 interpret these as the first appearance of the nucleoli of the 

 female pronucleus, the periphery of each ring representing 

 the chromatin of the chromosomes.^ If this interpretation is 

 correct, then the periphery of the vesicles which characterize 

 the later stages must be interpreted as chromatin, and the 

 spherical body in connection with each, as nucleolar substance. 

 These later stages are shown in photo. 26 (where three of 

 the eleven vesicles are represented) and in photos. 2^, 28, 29, 

 30, 31, and 32. In photo. 27 one of the vesicles shows thick 

 threads of chromatin connecting the nucleolus with the periph- 

 ery of the vesicle. 



Photo. 33 shows part of the head of the spermatozoon 

 breaking up into similar vesicles — the periphery of the vesicle 

 upon which we have focussed we interpret as of chromatin, 

 and the tiny spherical body as nucleolus. 



Photo. 34 shows a later stage of the development of the 

 spermatozoon into the male pronucleus, several of the vesicles 

 having fused into one, the rest being in adjacent sections. 



Osmophile Granules m the Nucleoli. 



It is exceptional to find osmophile granules in the nucleoli, 

 and we are therefore inclined to regard them as abnormal 

 features. A nucleolus from a germinal vesicle of an unstained 

 ovarian &g^ is shown in photo. 35. The ovary was fixed in 

 chromo-acetic, washed in water and immersed for one hour in 

 osmic in order to blacken the dentoplasmic granules. 



1 In these vesicles, at a little later stage of development, one of us differentiated 

 in color the nucleolus from the peripheral chromatin ring. Foot, " The Origin 

 of the Cleavage Centrosomes,"/<7?<;'«. of Morph., vol. xii, No. 3, 1897. 



